sys 6

Photosynthesis and Respiration Dynamics

• Seasonal Dynamics
    - Summer Months: More photosynthesis occurs than respiration, resulting in a net release of CO2 into the atmosphere.
        - Outcome: Increase in atmospheric O2 levels during summer months.
    - Fall and Winter Months: Photosynthesis halts as leaves drop, and respiration increases.
        - Outcome: Increase in CO2 levels in the atmosphere from November to May, decrease in atmospheric O2 levels.

• Hemispheric Differences
    - The observations primarily focus on the Northern Hemisphere due to:
      - Greater land mass contributing to higher levels of photosynthesis & respiration.
      - Measurements largely reflecting Northern Hemisphere gas circulation.
    - Southern Hemisphere exhibits opposite seasonal patterns in CO2 and O2 dynamics.

Keeling Curve and Longitudinal Data

• Charles David Keeling's Contributions
    - Initiated measurements of atmospheric CO2 in 1958.
    - Initial Measurement: 314 ppm CO2, during the industrial age, indicative of rising levels already above the historical threshold of 300 ppm.

• Trend Data
    - Continual rising trend of atmospheric CO2 from 1958 to present.
    - CO2 levels marked in years: 1991 and 2005 show significant increase.
    - By 2022, an increase of 10 ppm since 2020 illustrates ongoing trend.

Ice Core Data and Historical Context

• Ice Core Analysis
    - Ice core samples provide CO2 data stretching back 800,000 years, revealing historical atmospheric conditions.
    - Current CO2 levels are significantly higher than those recorded over the past 800,000 years.
    - Ice core data correlates strongly with Keeling's continuous measurement data, affirming the accuracy of both data sets.

• Historical CO2 Levels
    - Planet has historically experienced fluctuating and sometimes extreme CO2 levels well above 300 ppm.
    - Modern life evolved during a notably stable period compared to the geological history characterized by high variability.
  

Projections and Future Scenarios

• Future Projections for CO2 Levels
    - Various scenarios depict potential CO2 levels depending on mitigation actions:
      - Without mitigation, levels could rise to 2,000 ppm or higher.
      - More aggressive measures could stabilize the increase to 500 or 600 ppm.

Carbon Cycle Processes

• Photosynthesis and Respiration
    - Photosynthesis: Assimilation of inorganic carbon (CO2) into organic carbon by plants/algae.
    - Respiration: Mineralization process extracting energy from organic carbon and releasing CO2 into the atmosphere.

• Key Processes in Carbon Flux Model
    - Need to establish a pool-flux model for atmospheric CO2 to understand inflows and outflows:
      - Inflows: Cellular respiration (all organisms), burning fossil fuels, deforestation.
      - Outflows: Photosynthesis and ocean uptake.

• Human Impact:
    - Human activities like deforestation and burning fossil fuels affect both influx and outflux, leading to a rise in atmospheric CO2.

Carbon Pools and Fluxes

• Major Carbon Pools
    - Earth's crust: Large, largely inaccessible carbon reserve.
    - Oceans: Major carbon sink, taking in predominantly via physical and biological processes.

• Carbon Sink vs. Source Analysis
    - Terrestrial vegetation acts as a significant sink, netting about 120 gigatons of carbon from photosynthesis against 59 gigatons from plant respiration.
    - Oceans provide double as a sink despite complexity in their processes.

Human-Induced Changes to Carbon Cycle

• Deforestation:
    - Increases inflow of CO2 via burning or decomposing trees.
    - Decreases outflow by removing primary producers that sequester CO2.

• Burning Fossil Fuels:
    - A key source of CO2, releases contained geological carbon into the atmosphere, greatly increasing emissions.

• Annual CO2 Emissions Trends
    - Consistent upward trajectory in CO2 emissions over decades.
    - A notable dip in 2020 due to pandemic restrictions is temporary and does not indicate a long-term trend reversal.

Balancing the Carbon Cycle

• Equilibrium Model Requirements
    - Atmospheric CO2 levels can reach equilibrium when inputs equal outputs.
    - Decrease influx (pollution, land use change) and increase outflows (reforestation, carbon capture) are essential to stabilize atmospheric CO2 levels.

• Feedback Mechanisms
    - Negative feedback maintains equilibrium within the carbon cycle, e.g., increased respiration raises CO2 which promotes photosynthesis to lower CO2.
    - Positive feedback can arise, such as warming soils enhancing microbial respiration, further increasing atmospheric CO2.